Fairings are often mounted atop vehicle roofs to reduce air resistance or drag on trailers being pulled by vehicles, such as semi-tractors. The fairings serve to direct wind over and around the upper front flat portion of the trailers. This reduces the drag resistance transferred from the trailers to the vehicles and thereby improves the fuel economy of the vehicles.
Fairings are typically of either a unitary or a multi-piece design and may also include fairing extensions. The unitary fairings are often one-piece moldings of fiberglass. This results in fairings which are economical to make, lightweight, and structurally contiguous.
However, these unitary fairings are generally not adjustable in height which may lead to interference problems with overhead structures. When vehicles with fairings mounted on top thereof are being towed with either their front or rear wheels being held in a raised position, the overall height of the vehicle and fairing is increased. This towing may occur when a tow truck is hauling a disabled vehicle, or else, when a series of vehicles are being shipped in a piggyback fashion with one vehicle being mounted upon the fifth wheel of another vehicle.
Consequently, during towing, the elevated fairings may strike underpasses or tunnels they otherwise would pass beneath in normal vehicle operation. Accordingly, these unitary fairings may have to be removed during towing or shipping of vehicles to avoid interference problems and later be reattached.
Multi-piece fairings avoid this problem by being adjustable in height. When the vehicles are being towed, the overall height of the fairings may be decreased to avoid interference problems with overhead structures. Otherwise, during normal operation, the fairings are set at a greater height to direct air over and around trailers being pulled by the vehicles.
An example of a two-piece fairing is shown in U.S. Pat. No. 4,784,424. This particular device includes a bottom portion which is mounted to the roof of a vehicle and a top portion which is pivotally mounted for movement on the bottom portion so that the top portion may be received within the bottom portion in a folded storage position. At the rear of at least one of the top and bottom portions is a partial closure. Pivotal folding of the top portion relative to the bottom portion is accommodated by a hinge connecting the top portion to the bottom portion. The hinge may be a standard hinge such as a piano hinge or else a living hinge formed by cutting a single molded fairing into top and bottom portions while leaving an uncut portion therebetween which serves as the living hinge.
The fairing of U.S. Pat. No. 4,784,424 has a number of shortcomings. First, adding a hinge to the top and bottom portions adds mechanical complexity and expense to the manufacture of the fairing. Further, in the event the hinge rusts or otherwise deteriorates, the upper portion may become difficult to move between the raised position and the folded storage position.
In the case of the living hinge, load and stress are transferred across the uncut portion when the two portions are articulated relative to one another. Therefore, this joint is subject to failure if the uncut portion is subject to too high of loads. Also, if the uncut articulated joint is overly rigid or insufficiently flexible, movement between the top and bottom portions may be unduly limited.
Further, as the top and bottom portions are foldably joined or articulated together along their front ends, the front ends cannot move with respect to one another thereby limiting the allowable relative movement between the top and bottom portions.
Finally, replacement of the top or bottom portions is difficult. With the fairing employing the living hinge, the entire fairing must be replaced if the top or bottom portion becomes damaged. With the hinged fairing, the hinge must be disconnected and reconnected to the respective portions. If the hinge is corroded or rusted or otherwise damaged, replacement can be difficult.
Some of the above described problems encountered by previous fairing designs are addressed by the present invention which is summarized below.